The overall goal of this project is to increase understanding of the transcriptional regulation of vascular endothelial gene expression, especially during development of the embryonic vascular system. Ets family transcription factors have been strongly implicated in regulation of vascular endothelial gene expression and binding sites for Ets factors are present in the regulatory regions of most vascular genes. More recently several members of the kruppel-like factor (Klf) family of transcription factors have also been demonstrated to regulate expression of vascular genes. So far however, knockout of Klf genes in the mouse model has failed to demonstrate any requirement of Klf sequences for vascular development. Our studies of transcriptional regulation of the VEGF receptor gene, Flk-1, have revealed that a Klf binding site is essential for developmental expression of the Flk-1 gene. Furthermore, we have shown that expression of Klf2 in the frog embryo is sufficient to activate ectopic expression of vascular markers. We find that Klf2 protein physically associates with Erg, a vascular specific member of the Ets family and that Klf2 and Erg function synergistically to activate expression of vascular markers. Our central hypothesis is that Ets and Klf proteins cooperate to regulate expression of a large number of essential vascular genes. Cooperation of Ets and Klf family proteins is a novel observation that has important implications for vascular development and for gene regulation in vascular pathogenesis. The specific aims are: Aim 1. To determine the requirement for Klf factors for endothelial gene expression during embryonic vascular development and in mature endothelial cells. Aim 2. To determine the spacing and orientation of Ets and Klf DNA binding sites required for efficient transcriptional activation. Aim 3. To identify endothelial genes that are potential direct targets of Ets/Klf cooperative regulation. PUBLIC HEALTH RELEVANCE: Research in this proposal will study cooperation between two families of transcription factors (Ets and Kruppel-like factors - Klfs) in regulation of endothelial gene expression during early embryonic development. Results of these studies will increase understanding of the causes of congenital defects of human vascular development and improve our understanding of gene expression related to vascular pathology.